Paulownia seedlings were grown under 4 photoperiods—8, 12, 16, and 24 hours—for 97 days. Seedlings were harvested at intervals to determine the effect of photo-period on growth and development. Height growth and total dry matter production were significantly higher in the 16- and 24-hour photoperiods. The 8-hour photoperiod decreased root development. Seedlings grown in the 8-hour light period were more efficient photosynthesizers showing higher rates of net photosynthesis, lower respiration, and lower CO2 compensation points, and did not reach light saturation when compared with trees grown in longer photoperiods.